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Analysis of reactive bromine production and ozone depletion in the Arctic boundary layer using 3-D simulations with GEM-AQ: Inference from synoptic-scale patterns

by K. Toyota, J. C. McConnell, A. Lupu, L. Neary, C. A. McLinden, A. Richter, R. Kwok, K. Semeniuk, J. W. Kaminski, S. L. Gong, J. Jarosz, M. P. Chipperfield, C. E. Sioris show all authors
Atmospheric Chemistry and Physics ()

Abstract

Episodes of high bromine levels and surface ozone depletion in the\nspringtime Arctic are simulated by an online air-quality model, GEM-AQ,\nwith gas-phase and heterogeneous reactions of inorganic bromine species\nand a simple scheme of air-snowpack chemical interactions implemented\nfor this study. Snowpack on sea ice is assumed to be the only source of\nbromine to the atmosphere and to be capable of converting relatively\nstable bromine species to photolabile Br(2) via air-snowpack\ninteractions. A set of sensitivity model runs are performed for April\n2001 at a horizontal resolution of approximately 100 kmx100 km in the\nArctic, to provide insights into the effects of temperature and the age\n(first-year, FY, versus multi-year, MY) of sea ice on the release of\nreactive bromine to the atmosphere. The model simulations capture much\nof the temporal variations in surface ozone mixing ratios as observed at\nstations in the high Arctic and the synoptic-scale evolution of areas\nwith enhanced BrO column amount ({''}BrO clouds{''}) as estimated from\nsatellite observations. The simulated ``BrO clouds{''} are in modestly\nbetter agreement with the satellite measurements when the FY sea ice is\nassumed to be more efficient at releasing reactive bromine to the\natmosphere than on the MY sea ice. Surface ozone data from coastal\nstations used in this study are not sufficient to evaluate unambiguously\nthe difference between the FY sea ice and the MY sea ice as a source of\nbromine. The results strongly suggest that reactive bromine is released\nubiquitously from the snow on the sea ice during the Arctic spring while\nthe timing and location of the bromine release are largely controlled by\nmeteorological factors. It appears that a rapid advection and an\nenhanced turbulent diffusion associated with strong boundary-layer winds\ndrive transport and dispersion of ozone to the near-surface air over the\nsea ice, increasing the oxidation rate of bromide (Br(-)) in the surface\nsnow. Also, if indeed the surface snowpack does supply most of the\nreactive bromine in the Arctic boundary layer, it appears to be capable\nof releasing reactive bromine at temperatures as high as -10 degrees C,\nparticularly on the sea ice in the central and eastern Arctic Ocean.\nDynamically-induced BrO column variability in the lower-most\nstratosphere appears to interfere with the use of satellite BrO column\nmeasurements for interpreting BrO variability in the lower troposphere\nbut probably not to the extent of totally obscuring ``BrO clouds{''}\nthat originate from the surface snow/ice source of bromine in the high\nArctic. A budget analysis of the simulated air-surface exchange of\nbromine compounds suggests that a ``bromine explosion{''} occurs in the\ninterstitial air of the snowpack and/or is accelerated by heterogeneous\nreactions on the surface of wind-blown snow in ambient air, both of\nwhich are not represented explicitly in our simple model but could have\nbeen approximated by a parameter adjustment for the yield of Br2 from\nthe trigger.

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